The pressure gauge above the wet alarm valve has pressure, while the pressure gauge below has no pressure. What does this mean?

It stands to reason that the above table represents the pressure at the system end and the following table represents the pressure at the water supply end. If one of the meters is not accurate, either there is no water or insufficient pressure at the end responsible for the meter, or the pressure gauge is broken. The 04S206 in the second table atlas is connected by a check valve, but it is sometimes not connected in actual operation.

Generally speaking, the values of the two meters should be similar. According to the atlas, the two meters are connected by a check valve, which is used to supplement the pressure from the water supply end to the system end to prevent the false alarm caused by excessive pressure difference between the upper and lower ends. Therefore, if the pressure difference between the two meters is large, except that the water pressure in their respective systems is insufficient and the pressure gauge is broken, the check valve between the two meters is blocked, because the values between the two meters should be consistent.